In numerous uses, in particular for pharmaceutical uses, it is desirable to avoid incorporating preservatives in the fluid to be dispensed. To achieve that, there are two possible solutions. The first solution consists in using an airless system, i.e. a system which does not draw in any air. In which case, a fluid reservoir is provided whose volume decreases each time fluid is dispensed so as to compensate for the suction generated by a determined quantity of fluid being expelled. For example, this may be achieved by means of a flexible pouch that is emptied progressively, or by means of a follower piston disposed in the reservoir. The second solution is to treat or to filter the air drawn in each time fluid is dispensed. For this purpose, filtration elements are advantageously disposed in the intake air passageway in the dispenser pump or in the dispenser device. Thus, Document EP-0 189 549 discloses disposing a filter against the vertical side wall of the pump body that incorporates a vent hole. Document EP-0 800 869 discloses disposing a filter on the top edge of the neck of the receptacle. Document WO 97/18902 discloses disposing a filter inside the pump body between the piston and said pump body.
The systems described above suffer from the major drawback of being complicated to implement. It is necessary to modify at least one component part of the pump or of the dispenser device incorporating said pump, and assembly is therefore made more complex. The manufacturing and assembly cost is thus increased.